The major objectives of this application are to: (i) functionally characterize a signal transduction pathway linking ATM (ataxia-telangiectasia-mutated) to the cyclic AMP response element-binding protein (CREB) transcription factor;and (ii) identify and functionally characterize novel ATM substrates. ATM is a DNA damage-activated protein kinase that is mutated in the genetic instability and neurodegeneration syndrome, ataxia-telangiectasia, whereas CREB is a neuroprotective transcription factor that regulates cell growth, metabolism, and survival. We have defined a new mode of CREB regulation whereby ATM and casein kinases 1 and 2 (CK1/CK2) collaboratively phosphorylate CREB on five clustered sites termed the RAX domain (co-Regulated ATM and Casein Kinase Sites) in response to genotoxic stress. Phosphorylation of CREB by ATM and CK1/CK2 inhibits the interaction between CREB and its coactivator, CREB-binding protein (CBP) suggesting that the ATM pathway may repress CREB transcriptional functions in response to DNA damage. The linkage between ATM and CREB is intriguing given the neuroprotective functions of both factors. In this proposal we will test the hypothesis that ATM plays a dual role in CREB regulation through suppression and stimulation of RAX domain phosphorylation in unperturbed and DNA-damaged cells, respectively. An important goal of the work is to define the upstream signals controlling CREB RAX domain phosphorylation in the absence of DNA damage and to elucidate the biochemical outcomes of its modification in intact cells. In addition, we will use information gleaned from the CREB phosphorylation paradigm to discover and functionally characterize protein substrates that are coordinately regulated by ATM and CK1/CK2 in response to DNA damage. These studies should yield fundamental insights into the mechanisms of ATM function and CREB regulation, and may alter current views of ATM signaling in response to DNA damage. The goal of this project is to understand the molecular basis for the neurodegeneration/cancer susceptibility syndrome, ataxia-telangiectasia (A-T), which is caused by mutations in the ATM gene. ATM is a critical regulator of cellular responses to DNA damage and the work proposed in this application will characterize a particularly important downstream target of ATM, termed CREB (cyclic AMP response element-binding protein), which is an important regulator of gene expression. We are specifically interested in examining whether deregulation of CREB contributes to the manifestation of A-T-related phenotypes, including cancer, and neuron demise.